NEW YORK (AP) -- Joan Rivers' loved ones said Sunday that they remain hopeful about her recovery three days after she went into cardiac arrest at a doctor's office. "We are keeping our fingers crossed," her daughter, Melissa Rivers, said in a statement, thanking people who have expressed support for the 81-year-old comedian. Rivers on Friday described her mother's condition as serious. Joan Rivers was taken to Mount Sinai Hospital on Thursday, a day after she spoke at an employee event at Time Inc. in New York. Spectators there said she had appeared to be well. Rivers is the host of "Fashion Police" on E! and presides over an online talk show, "In Bed With Joan." She also co-stars with her daughter on the WEtv reality show "Joan & Melissa: Joan Knows Best?" Two of her "Fashion Police" co-stars tweeted their well-wishes to Joan Rivers and her family Saturday. "Praying for Joan Rivers and Mel Rivers," Giuliana Rancic tweeted. "Even though Joan's the strongest woman I know, every single prayer counts. I love you, Joan." "4 the first time in years I got down on my knees & prayed tonight!" Kelly Osbourne wrote. "I encourage U 2 do the same 4 Joan Rivers my grandma!"